For those looking for an entirely programmatic (or at least server-side) solution, I've had great success using catdoc's xls2csv tool.
Install catdoc:
apt-get install catdoc
Do the conversion:
xls2csv -d utf-8 file.xls > file-utf-8.csv
This is blazing fast.
Note that it's important that you include the -d utf-8
flag, otherwise it will encode the output in the default cp1252
encoding, and you run the risk of losing information.
Note that xls2csv
also only works with .xls
files, it does not work with .xlsx
files.